Is it possible to convince this mod to treat train wagons as part of a logistics network? So allow logibots to directly pick up or drop off items? It would essentially be like setting up logistics and trash slots but on a train wagon.

That's a fair bit outside the scope of adding equipment grids.

You may find what you want with this mod: https://mods.factorio.com/mod/logistic-cargo-wagon
Maybe he'd be willing to to add an equipment turning any wagon into logistic wagons.

Thanks Optera.

Since 1.0 and with the spidertron addition it would be really helpful to have such an equipment. With it you could simply go to a base and refill your building spidertron automatically.

I am just testing this one: https://mods.factorio.com/mod/EquipmentGridLogisticModule
It seems to work fine for the spidertron. Just don't forget to pin the module (set filter), or it will be trashed immediately ;)

@ CyberMarla yes found the mod already works great. It is a bit insensitive because you can only request whole stacks but it works great.

The vehicle grid has much unused potential though. I found only increased versions of existing equipment in other mods. I would like a radar for example.

I once tried turning VehicleRadar into using equipment radar, but performance was terrible.
Using a normal radar as update trigger for revealing chunks with vehicles is much better for performance.